1.18 – Cellular Respiration
The transfer of chemical energy from glucose to
ATP
Aerobic cellular respiration – uses oxygen and
produces large amounts of ATP
Anaerobic cellular respiration – doesn’t use
oxygen and produces small amounts of ATP
Humans rely mainly on aerobic cellular
respiration
Aerobic Cellular Respiration
Occurs in 2 stages:
1. Glycolysis
A series of reactions in the cytoplasm of a cell that
breaks a glucose molecule (C6H12O6) into 2 pyruvate
(C3H6O3) molecules and forms 2 molecules of ATP
• ATP is produced by attaching a phosphate
molecule to ADP
The reactions in glycolysis release energy (they
are exergonic)
The formation of ATP absorbs energy (it is
endergonic)
The equation for glycolysis is:
C6H12O6 --------------------------------------→ 2 C3H6O3
Glucose
2 Pyruvate
2. Oxidative Respiration (Krebs Cycle)
A series of reactions occurring in the
mitochondria that uses the oxygen to convert
pyruvate into carbon dioxide, water, and ATP
6 molecules of CO2 and 6 molecules of H2O are
produced
34 molecules of ATP are produced
The equation for oxidative respiration is:
2 C3H6O3 + 6 O2 ---------------------→ 6 CO2 + 6 H2O
Something to Note:
The overall process of aerobic cellular
respiration produces 36 ATP total:
2 ATP from glycolysis + 34 ATP from oxidative
respiration = 36 ATP total
Therefore, the overall equation for aerobic
cellular respiration looks like this:
C6H12O6 + 6 O2------------------→ 6 CO2 + 6 H2O
Anaerobic Respiration
Occurs when oxygen is not available
Happens through a series of reactions called
fermentation
• There are 2 types of fermentation:
1. Ethanol Fermentation
Occurs in the cytoplasm of yeast cells
The steps in this process are:
• Glucose is broken down during glycolysis → 2
pyruvate and 2 ATP
• An enzyme in the cytoplasm called pyruvate
decarboxylase removes a CO2 molecule from
pyruvate, converting it into ethanol (found in
alcoholic beverages)
• The ATP is used for evergy, and the CO2 and
ethanol are released as waste
The overall products are: 2 ATP (glycolysis), 2 CO2, 2
ethanol
2. Lactic Acid Fermentation
Occurs in human muscle cells during strenuous
exercise when glucose gets broken down faster
than oxygen can be supplied
The steps in this process are:
• Glucose is broken down during glycolysis → 2
pyruvate and 2 ATP
• An enzyme in the cytoplasm called lactate
dehydrogenase converts pyruvate into lactate
• The ATP is used for E, the lactate accumulates in
the muscles causing stiffness, soreness, and
fatigue
When there is enough oxygen, lactate is
converted back to pyruvate, which goes back to
the mitochondria and goes through oxidative
respiration
The extra O2 needed during exercise is referred
to as oxygen debt
Photosynthesis and Cellular
Respiration
Plants use CO2 for photosynthesis, animals give
off CO2 as a waste product of cellular respiration
Plants give off O2 as a byproduct of
photosynthesis, animals use O2 in cellular
respiration
Reveals a relationship between autotrophs and
heterotrophs
Homework
• Page 82 # 1-8